Table 2. Potential causes of an isolated prolongation of the APTT.

Cause	History of bleeding	Hemorrhagic symptoms	Mixing test
Congenital clotting factors deficiencies
Factor XII deficiency	Usually absent	Absent	Correction
Factor VIII deficiency	Highly suggestive	Present	Correction
Factor IX deficiency	Highly suggestive	Present	Correction
Factor XI deficiency	Suggestive	Variably present	Correction
Acquired haemophilia	Usually absent	Present	No correction
Heparin therapy	Usually absent	Variably present	No correction
Lupus anticoagulant	Usually absent	Absent	No correction

APTT, activated partial thromboplastin time.